rpm: fix installation warning (#479)

Avoid cosmetic error when installing the package:

 line 8: cho: command not found

packages/rpm/n2n.spec.in

@@ -78,7 +78,7 @@ if ! grep -q n2n /etc/group; then
 fi
 
 if ! /usr/bin/id -u n2n > /dev/null 2>&1; then
-  cho 'Creating n2n user'
+  echo 'Creating n2n user'
   /usr/sbin/useradd -M -N -g n2n -r -s /bin/false n2n
 fi